Descriptions will be given of problems of an examination technique for a case of manufacturing a semiconductor device on a semiconductor wafer. A semiconductor device is manufactured by repeating a step to transfer a pattern formed on a photo mask onto a semiconductor wafer by a lithographic processing and an etching processing. In the process for manufacturing a semiconductor device, the quality of, e.g., a lithographic processing and an etching processing and the occurrence of a foreign substance have a significant influence on a yield of the semiconductor device. Thus, early or previous detection of an abnormality or a defect in the manufacture processing is important. Accordingly, in the manufacture process, a pattern formed on a semiconductor wafer is measured and examined.
Particularly, due to recent development of miniaturizing and three-dimensionally forming a semiconductor device, managing overlaying patterns in different processes becomes more important. Conventionally, in order to determine an overlay misalignment amount of patterns between different process steps, a semiconductor device is irradiated with a light and a position of a pattern manufactured in each step is measured based on a reflected light from the semiconductor device.
However, due to miniaturizing of a pattern, a light hardly obtains a required accuracy. Needs for measurement of an overlay misalignment amount with use of a scanning electron microscope, which has a higher resolution than a light, are increasing. For example, Patent Literature 1 proposes a method for measuring a misalignment amount between two patterns formed by double patterning with a scanning electron microscope. In Patent Literature 1, two patterns formed on a surface of a semiconductor device are measured. Thus, a scanning electron microscope can easily acquire images of those patterns.
On the other hand, to measure an overlay misalignment amount between a pattern formed on a surface of a semiconductor device and a pattern formed inside the semiconductor device, respective favorable images of the surface pattern and the inside pattern are required to be obtained. Generally, while a secondary electron from a sample includes much information of the surface, information of the inside structure is mainly reflected in a back scattered electron. Patent Literature 2, for example, describes a scanning electron microscope capable of detecting a secondary electron and a back scattered electron, separately. Patent Literature 3 discloses a technique to improve a contrast of a lower layer pattern with use of detection signals from multiple detectors. Patent Literature 4 discloses a technique for acquiring pattern images of different layers with two light sources having different irradiation energies and displaying the pattern images alternatively or substantially in an overlaid manner.